Wot is it?

[Ludwig II]

I know, but who else does?

 

[maurtis]

Looks like this: Bugatti T72A

(I cheated and Google image searched for "single cylinder under bike engine" LOL)

 

[Ludwig II]

You unspeakeable devil! Right, your turn, find us something obscure.

 

[maurtis]

Don't think this is all that obscure, but my jaw dropped when I saw it...

 

[Ludwig II]

I do know what it is, so I'l leave it for others. They used to race them.

 

[Ludwig II]

Come on, somebody, or I'll answer it and post a real stinker afterwards.

 

[Ludwig II]

OK, since we have been deluged with answers, I'll tell you. It's a Megola. The engine rotates with the front wheel. There's no gearbox and no clutch, but in the late 20s they were raced in German 1,000 metre longtrack dirt races.

Overall ratio changes require fitting different size rims to the wheel assembly.

 

[Ludwig II]

Next one, made by a still extant manufacturer for a client before they decided to make their own individual way forward.

 

[Ludwig II]

And what exactly is this flat twin?

 

[LouieMCman]

Easy...Indian Model O (or Nothing!)

 

[Ludwig II]

What's the b & w above it?